Strip heating apparatus



STRIP HEATING APPARATUS Frederic 0. Hess, Philadelphia, Pa., assignor to Selas Corporation of America, a corporation of Pennsylvania Application September 24, 1956, Serial No. 611,790

14 Claims. (Cl. 2633) The present invention relates to apparatus for the continuous heating of strip material, and more particularly to a construction by which the hot gases of combustion released from the heating chamber can be directed over given portions of the strip for preheating purposes.

In the continuous heating of a strip material for various purposes, such as the annealing of strip steel for example, it is customary to move the strip vertically downward through a preheating zone of a furnace, and then through a heating zone or zones. The products of com bustion from the heating zone flow upwardly to preheat the strip as it is moving through the preheating zone. Due to the normal heating characteristics of strip material the edges of the strip are more readily heated than the center. Therefore as the strip is preheated by the freely flowing gases the edges are heated to a higher temperature than is the center. This initial uneven heating of the strip across its width in many cases makes it difficult if not impossible to heat the strip uniformly across its width when it later moves into the heating zone.

Itis an object of the invention to provide a method and apparatus for preheating strip material in which the strip is preheated unevenly across its width in order to facilitate the final production of an evenly heated strip.

it is a further object of the invention to provide apparatus which will direct combustion gases in concentrated convective heating relation over selected portions of a strip of material that is being heated.

It is a further object of the invention to provide apparatus for rapidly and continuously heating strip material evenly from edge to edge.

Strip material, such as thin tin plate steel stock, for example, is more readily heated and cooled at the edges than it is at the center. This characteristic is due to the fact-that the edges of the strip have more surface area than does the center. According to the present invention more of the hot exhaust gases are directed into convective heating relation with the center of the strip than with the edges. Thus the center is preheated to a higher degree than the edges. Therefore the final heating of the strip can be uniform from edge to edge to bring the entire width of the strip up to temperature at the same time.

The apparatus and method of this invention are also useful in heating strip that is not of uniform thickness from edge to edge, as well as for heating strip to different temperatures across its width if this is desirable for some reason.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In'the drawings:

"atent C Fig. 1 is a section view through a furnace of the present invention,

Fig. 2 is a section across the pre-heating chamber taken on line 2-2 of Fig. 1,

Fig. 3 is a section showing the face of one of the walls of the preheating chamber taken on line 33 of Fig. 2, and

Fig. 4 is a section similar to Fig. 2 showing a modified form of the invention.

The furnace shown herein by way of illustration is of the type disclosed in Bloom application Serial No. 509,633, filed February 19, 1955. This furnace includes an elongated furnace structure '1 that is built in accordance with ordinary furnace practice and which is U- shaped in section. The space between the outer ends of the U is closed by a door 2 to form a furnace chamber which is substantially rectangular in cross sections The door is hinged to the end of one of the legs of the U by a suitable hinge shown at 3. This construction produces a narrow, elongated furnace chamber in which the side walls thereof face the strip 4 and are in proximity thereto as the strip passes through the furnace from the top to the bottom. The furnace chamber is slightly wider than the width of the widest strip that is heated therein.

The furnace structure is provided at its upper end with a preheating zone 5 and its lower end with a heating zone 6. The entire structure is adapted to be moved to the left in Fig. 2 of the drawing away from the strip when for some reason the heating is stopped. As this movement takes place door 2 is automatically opened just as the furnace begins to move and is closed when the moving is completed, with the furnace away from the strip, in order to prevent loss of heat.

The furnace moves between a'lower structure 7 that is provided with seals 8 between it and the furnace, and an upper stack structure 9 that is connected with suitable exhaust ducts 10 through which the products of combustion produced in the furnace are removed. Seals 11 are provided between the upper end of the furnace and the stack structure.

Apparatus for moving the furnace, which forms no part of the present invention, is disclosed in the abovementioned Bloom application. It is noted, however, that the frame 12 of the furnace has a plurality of wheels13 extending from each side at the upper end thereof. These wheels roll along tracks 14 that are mounted on suitable structural supporting members 15.

The walls in the heating zone 6 of the furnace include aplurality of panel members 16 that are suitably held in place in frame 12. Each of these panel members is provided on its inner face with a plurality of rows of burners -17 of the type disclosed in Hess Patent 2,215,079, issued September 17, 1940. These burners are characterized by the fact that a combustible mixture of fuel and air is burned in a cup-shaped depression formed in-the face of the furnace wall to heat these depressions to incandescence. Radiant heat from the depressions as well as convection heat from the hot products of combustion that are released serve to heat the trip as it is being moved continuously through the furnace chamber. The design is such that the strip will be heated to the proper temperature by the time that it passes into exit structure 7. It is noted that the horizontal rows of burners in each of the panels are offset with respect to each other, as shown for example in Fig. 3, so that the radiation produced thereby will be overlapping from onerow to the other in order to produce an even heat pattern from side to side of the furnace chamber.

The preheating zone 5 lies above and connects with heating zone 6 and is narrower than the heating zone.

The products of combustion preheat the strip by convec'tion'as they pass upwardly through zone 5 to the stack in counterflow to strip movement as the strip moves through this zone. Due to the fact that the edge of a stri has more surface for receiving heat than the center of the strip, diificulty has been experienced in heating the center to the same temperature as the edges. In accordance with the present invention the walls of the preheating zone are so shaped that the portion of the walls 18 opposite the edges of the strip are relatively close thereto, while the portions of the wall 19 that are opposite the center of the strip are at a larger distance from the strip surface. The end portions of the preheating zone are also enlarged as shown at 21. Therefore the combustion gases which transfer heat to the strip in the preheating zone pass in a larger quantity through the enlarged portions within the curved section 19 than pass through the narrow portions between the surfaces 13. Also more gases pass'beyond the edge of the strip in the portions 21 than can move in contact with the edges. The lower ends of the surfaces 18 are curved as shown at 22 in Fig. 3 in order to direct the upwardly flowing gases of combustion into the portions 19 and 21.

In the operation of the furnace the burners are fired to heat rapidly and progressively the strip as it is moving through heating zone 6. The hot products of combustion produced by the burners rise through the preheating zone. More of the products of combustion pass the center portion of the strip than pass the edge portions thereof. This channelling of the gases to the center of the strip and away from the edges thereof serves to preheat the center portion of the strip to a higher degree than the edges. When the strip reaches the heating chamber, which is heated evenly from side to side, the heating characteristics of the strip will cause it to absorb more heat at the edges than at the center. Since the center was preheated more than the edges, the additional heat absorbed by the strip during its passage through the heating zone will even out, so that by the time the strip leaves that zone it will be heated evenly from edge to edge.

From time to time strip is encountered that is thicker at the center than it is at the edges. Such strip, to be heated evenly, requires more heat at the center than at the edges in proportion to the additional thickness at the center. The configuration of the side walls of the preheating chamber described above will assist in accomplishing this.

By changing the contour of the walls of the preheating chamber the strip can be heated in some given pattern in varying amounts across its width without altering the pattern of the burners, or the amount of fuel that is supplied thereto. For example, referring to Fig. 4, it will be seen that the side walls of the preheating chamber facing the strip are shaped to provide a plurality of ridge portions 23 that are close to the strip and a plurality of depressed portions 24 that are remote from the strip.

Thus the products of combustion will be channelled through the depressed portions 24 to preheat the strip with relatively hot and cool streaks across its width. There after in the heating zone of the furnace, the temperature of each portion of the strip will be raised a predetermined amount so that finally as the strip leaves the heating zone it will be heated varying degrees across its width depending upon the contour of the preheating zone walls.

From the above description it will be seen that I have provided a method and apparatus for preheating a strip of material in such a manner that it can be heated evenly across its width or in varying degrees across its width depending upon the desired product. Thus evenness or variation in the final strip temperature can readily be obtained by shaping the walls of the preheating zone so that more or less of the combustion gases from the heating zone are channelled into convective heat relation with various portions of the strip. The necessary contours of the walls of the preheating zone can easily be formed by the shapes of the bricks used to build the Wall 4 of this zone or by using suitable forms if the wall is made of a cast refractory.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention as set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

What is claimed is:

1. The method of heating continuously a strip of material which comprises moving the strip downwardly through a preheating zone and then a heating zone, heating the strip in the heating zone by radiant and convection heat produced by combustion of fuel and combustion supporting gas in the presence of the strip, moving the products of combustion upwardly from the heating zone through the preheating zone in convective heating relation with the strip, and varying the thickness of the layer of said products of combustion from one portion of the strip to another across the width thereof.

2. The method of heating continuously a strip of material which comprises moving the strip downwardly through a preheating zone and then a heating zone, heating the strip in the heating zone by radiant and convection heat produced by combustion of fuel and combustion supporting gas in the presence of the strip, moving the products of combustion upwardly from the heating zone through the preheating zone in convective heating relation with the strip, and moving a greater volume of products of combustion past one portion of the strip than past another portion thereof acros sthe width of the strip.

3. The method of heating strip material continuously which comprises moving the strip continuously through a preheating zone and a heating zone, heating the strip in said heating zone with radiant heat and convection heat produced by burning a combustible fuel mixture in the presence of said strip, moving the gaseous products of combustion from the heating zone through the preheating zone, and channelling the combustion gases as they pass through the preheating zone in such a manner that a thicker layer of gases are beside one portion of said strip than are beside another portion thereof across the strip.

4. The method of heating strip material continuously which comprises moving the strip continuously through a preheating zone and a heating zone, heating the strip in said heating zone with radiant heat and convection heat produced by burning a combustible fuel mixture in the presence of said strip, moving the gaseous products of combustion from the heating zone through the preheating zone, and directing the gases as they pass through the preheating zone in such a manner that they will transfer more heat to the center portion of the strip than to the edge portions thereof to thereby preheat the center of the strip a greater amount than its edges.

5. Strip heating apparatus comprising in combination structure forming an elongated heating chamber having sides thereof closely adjacent to the opposite surfaces of a strip of material passing lengthwise therethrough, burners in said sides operative to heat the strip by the combastion of fuel with the combustion gases enveloping the strip, structure forming a preheating chamber surrounding the strip and in open communication with the heating chamber at the entrance end thereof, the sides of said preheating chamber facing the surfaces of said strip being curved to present portions thereof across said strip that are different distances from the surfaces thereof, said portions extending lengthwise of the strip.

6. The combination of claim 5 in which the portions of the wall of said preheating chamber that are closest to the Strip are adjacent the edges thereof,'and the portions of the wall of said preheating chamber that are most distant from the strip are opposite the center thereof.

7. The combination of claim 5 in which the portion of the walls of said preheating chamber that face the sur-- wise of the chamber to form channels parallel to the strip and extending lengthwise thereof through which heating gases may flow, and means to supply heating gases to flow lengthwise through said chamber.

9. The combination of claim 8 in which the portions of said walls closest to the strip are adjacent to the edges thereof.

10. The combination of claim 8 in which said Walls are configured to form a plurality of channels on each side of the strip.

11. Apparatus for the continuous heating of strip material comprising in combination a vertically disposed, elongated furnace of substantially rectangular section having a preheating zone and a heating zone in open heating zone communication with each other and through which the strip passes in sequence, said heating zone being provided with sides substantially parallel to the surface of the strip, burners firing in said heating zone to heat the strip, the products of combustion rising through said preto preheat the strip, the sides of said preheating zone being provided with a plurality of surfaces extending parallel to the travel of the strip through the furnace, some of said surfaces being closer to the surface of the strip than other of said surfaces.

12. The combination of claim 11 in which the surfaces of said preheating zone closest to the surface of said strip are opposite the edges thereof, and the surfaces of said preheating zone most remote from the surface of the strip being opposite the mid portion thereof.

13. The combination of claim 11 in which adjoining surfaces of said preheating zone are alternately close to and more remote from the surface of the strip.

14. The combination of claim 13 in which some of said surfaces of the preheating zone closest to the strip are opposite the edges thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,673,080 Hepburn et a1 Mar. 23, 1954 FOREIGN PATENTS 890,055 Germany Sept. 17, 1953 

